Pend Oreille, Lakelake in Kaniksu National Forest, northwestern Idaho, U.S. The largest lake in Idaho, it is about 40 miles (65 km) long and 4 miles (6.5 km) wide and covers an area of some 125 square miles (325 square km). It is about 21,500 150 feet (760 350 metres) deep and is noted for the highly prized Kamloops rainbow trout. The lake (the name of which is derived from the French name [Pend d’Oreille] for the Kalispel Indians, who wore ear pendants) receives the Clark Fork River, which becomes the Pend Oreille River when it leaves the lake.